fixed incorrect type custing (fixed problem with runing tests with --debug...

fixed incorrect type custing (fixed problem with runing tests with --debug (thanks, Sergei Gluhov spoted it))

mysql-test/r/view.result

@@ -1329,6 +1329,18 @@ update v1,t1 set v1.s1='c' where t1.s1=v1.s1;
 select * from v1;
 s1
 c
+prepare stmt1 from "update v1,t1 set v1.s1=? where t1.s1=v1.s1";
+set @arg='d';
+execute stmt1 using @arg;
+select * from v1;
+s1
+d
+set @arg='e';
+execute stmt1 using @arg;
+select * from v1;
+s1
+e
+deallocate prepare stmt1;
 drop view v1;
 drop table t1;
 create table t1 (a int);

mysql-test/t/view.test

@@ -1297,6 +1297,14 @@ update v1 set s1='b';
 select * from v1;
 update v1,t1 set v1.s1='c' where t1.s1=v1.s1;
 select * from v1;
+prepare stmt1 from "update v1,t1 set v1.s1=? where t1.s1=v1.s1";
+set @arg='d';
+execute stmt1 using @arg;
+select * from v1;
+set @arg='e';
+execute stmt1 using @arg;
+select * from v1;
+deallocate prepare stmt1;
 drop view v1;
 drop table t1;
 

sql/sql_update.cc

@@ -80,9 +80,8 @@ static bool check_fields(THD *thd, List<Item> &items)
       we make temporary copy of Item_field, to avoid influence of changing
       result_field on Item_ref which refer on this field
     */
-    field= new Item_field(thd, field);
-    it.replace(field);
-    ((Item_field *)item)->register_item_tree_changing(it.ref());
+    it.replace(new Item_field(thd, field));
+    field->register_item_tree_changing(it.ref());
   }
   return FALSE;
 }